Titel: Birds in southern Öresund in relation to the wind farm at Lillgrund
Författare: Leif Nilsson, Martin Green
Utgivare: Vattenfall, Lunds University
Årtal: 2011
Ämnesord:Lillgrund, Vattenfall, Eider, Red-breasted Merganser, Long-tailed Duck, Herring Gull, Cormorant, migration
Rapport via Vattenfall
Summary: This report presents the results of the monitoring programme for Lillgrund offshore wind farm. Base-line studies were undertaken during 2001-2006 (Green & Nilsson 2006, see also Nilsson 2001 for background information). According to the original plans the studies should be continued for three seasons after the wind farm was set in operation but due to problems with the data collection during cold periods this was extended to four seasons, i.e. 2007/09- 2010/11.
Staging and wintering birds in the area were surveyed both from boat and from the air. Boat
counts covered the area from the Öresund Bridge over Lillgrund to Bredgrund south of the
wind farm. Aerial surveys covered a larger area from the bridge to the shallow areas south of the Falsterbo peninsula. The aim of the aerial surveys was to cover a larger area than the wind farm and its neighbourhood, and the areas south of Falsterbo were included as a reference area. In all 19 boat counts were made during 2001-2005, and 8 in 2007-2011, whereas five aerial surveys were undertaken in 2004 and 2006 and 15 in 2008-2011.
The numbers of staging and wintering waterbirds showed a large variation between seasons and years both during the base-line studies and during the surveys after the establishment of the wind farm. This kind of variation is well-known from other surveys of seabirds in offshore waters. Three species of diving ducks dominated the bird fauna of the wider Lillgrund area: the Eider Somateria mollissima, the Red-breasted Merganser Mergus serrator and to a smaller extent the Long-tailed Duck Clangula hyemalis. Two other species occurred in larger numbers in the same area: Herring Gull Larus argentatus and Cormorant Phalacrocorax carbo. Other seabirds were only found in smaller numbers and the analysis was focused on the possible effects of the wind farm on the five mentioned species.
The population of Red-breasted Merganser in the area is the largest concentration known
from the country and the area is an internationally important wintering area with a large
proportion of the entire Baltic (and Northwest European) population. Eiders winter in
relatively large numbers in the southern Öresund and around Falsterbo (reference area). The species also has a large colony on Saltholm and the area is also much used as stopover area during spring migration. The third seaduck species, the Long-tailed Duck, occurs regularly in much smaller numbers, the main wintering area for this species is in the Baltic proper.
The surveys did not show any larger changes in numbers of staging and wintering water birds in southern Öresund that could be related to the establishment of the wind farm. Locally, Long-tailed Ducks and Eiders were found to avoid the actual wind farm area at least initially. For Eiders there were signs of habituation, especially during the last study season. During the first three years with the farm in operation only single birds or small groups were seen in the wind farm area, but during the last surveys in 2011 larger flocks were recorded on the water within the wind farm. The patterns for Red-breasted Mergansers were less clear and numbers using the whole area were lower during the post- compared to the pre-construction period.
Cormorants and Herring Gulls were seemingly not affected at all by the presence of the wind farm. For Herring Gulls an avoidance of the wind farm is implied by some of the results, but this is most likely not an effect of the wind farm as such but instead of the absence of fishing vessels within the wind farm in the post-construction period.
The bird migration over the area was studied with surveillance radar. The radars used in this study cover birds migrating in flocks, but not birds migrating singly. Furthermore, the larger the birds and/or the flocks, the better they are covered by these radars. This means that the migration patterns studied here mainly concern birds such as waterbirds and pigeons. Dense passerine migration is also covered during some days, but it is more uncertain to what extent the passage of for example raptors over the area is covered. In all, radar data were analysed for five spring seasons (2001 and 2005 pre-, 2008, 2009 and 2010 post-construction) and three autumn seasons (2001 pre- and 2008 and 2009 post-construction). No larger changes inthe migration patterns were found, neither during spring and autumn nor during day and night, that could be related to the construction of the wind farm at Lillgrund. On the other hand the fraction passing over Lillgrund since the wind farm was established was only about 20 % of the proportion passing before the wind farm was built. We interpret this as that most birds avoid flying through the wind farm area. This avoidance reduces the risk for the birds to come into conflict with the wind farm. The collision risks are probably small, at least for the birds that can be followed by surveillance radar. We estimate that somewhere in the order of between 100 and a few hundred individual birds may collide with (and get killed by) the wind farm at Lillgrund. This is about a tenth of the numbers probably colliding with (and getting killed by) the nearby Öresund Bridge.